1. Field of the Invention
The present invention relates to implants, and, more particularly, to orthopaedic implants.
2. Description of the Related Art
A number of solid metal and resorbable polymer (e.g. PLLA, PGA) screws are known. These screws are generally meant to provide short term (9 months or less) attachment of the soft tissue to the bone until healing and integration can occur.
There are a number of problems associated with the known metal and resorbable screws. Due to the density of the metals that are used in the solid metal screws, it is difficult to examine bone or soft tissue that is near the screw via x-ray, CT, or MRI scan. The screw causes a significant ‘white-out’ in the region of the screw. Tissue healing and integration around the screw is critical to the success of the surgery, thus the ability to evaluate the tissue near the screw is valuable. In addition, the solid metal screws have issues with poor initial fixation and later pull-out of the soft tissue (e.g. pull out of an ACL from the bone) does occur. These are painful and can require follow-up surgery. Certainly any improvements to reduce the rate of pull-out and additional surgery would be desirable.
With respect to the known resorbable screws, issues with poor initial fixation and pull-out also exist. The rate of resorbtion of the polymer can be difficult to control and can occur too quickly for a given patient, increasing the risk of soft tissue pull-out. Further, resorbable materials have been shown to induce fibrous tissue formation between the resorbable implant and the bone, increasing the risk of soft tissue pull-out. This may be due to the local chemistry created as the polymer dissolves.
Further, one individual may need to undergo multiple surgeries on a given joint. However, the more material and/or hard material that remains relative to an orthopaedic implant, the greater the difficulty that material can cause in future surgeries.
What is needed in the art is an orthopaedic screw that allows for more effective fixation of the tissue and visualization with known imaging devices of the tissue near and surrounding the screw. Further, what is needed in the art is an orthopaedic internal fixation device which includes at least two different structural materials, one such structural material being non-resorbable relative to a corporeal body.